This invention relates to repertory diallers, such as used in telephone subscriber's instruments. It should be noted that the term dialler as used herein is intended to cover wanted digit sending in response to push-button operation as well as in response to the operation of the rather older-established rotatable dial.
In some cases while dialling a wanted number, one receives an additional dial tone during number sending. When this occurs when dialling manually, after dialling a first portion of the number, it is necessary to await the next dial tone and then continue dialling. A common circumstance in which this occurs is when "dialling out" from a PABX to another PABX, or to the public switched telephone network (PSTN).
When dialling out from a PABX it is necessary to dial an access code and then await the second dial tone before sending the rest of the wanted number. Many repertory diallers currently in use permit the storage of access pause codes, i.e. codes which define access pauses, as part of the stored number. An example of this is described in our British Pat. No. 1446024 (A.C. Beadle et al 33-13). In the arrangement described herein the pause, which may be of fixed or variable duration, is inserted at the correct position when dialling out from the repertory store, to ensure reception of the second dial tone before continuing with the dialling sequence. In the above-quoted Patent, the pause is variable since a dial tone detector checks for the presence of the second dial tone and permits completion of the dialling in response to reception thereof.
However, when the subscriber makes a call to the PSTN via a PABX, he does not normally key or otherwise send an access pause code: the pause is generated naturally by listening for the second dial tone before continuing with the signalling. If this number is then retained for redial or repeat of the last number (RLN) usage, it does not contain the required access pause code.
One way to overcome this problem which is currently used is for the subscriber to dial (or key in) the access code digit manually, wait for the second dial tone and then, after the remainder of the number has been dialled, operate the redial or RLN facility. Special circuitry ensures that any digits corresponding to manually dialled access code digits are removed from the stored number before it is signalled to the PSTN. This involves a degree of complication due to the special circuitry referred to above. An object of the invention is to provide an improved and less complicated solution to the access pause code problem.